Article Posted on : - Apr 11, 2010

NASA astronaut Clayton Anderson, STS-131 mission specialist, participates in the mission's first spacewalk as construction and maintenance continue on the International Space Station. A NASA Photo.

CAPE CANAVERAL, FLORIDA (AP): Astronauts struggled with stiff bolts while attaching a big new tank full of ammonia coolant to the International Space Station on Sunday, their second spacewalk in three days to accomplish the job.

The action unfolded on the 40th anniversary of the launch of Apollo 13.

Using a combination of robotics and spacewalking expertise, Discovery’s crew members installed a new Ammonia Tank Assembly (ATA) on the International Space Station’s Starboard 1 truss. Mission Control verified that electrical connections with the ATA are working. Because of a troublesome bolt, the spacewalkers fell behind the timeline and were unable to complete all the scheduled work. Tasks that were deferred from today’s spacewalk include fluid connections to the ATA and the retrieval of two micrometeoroid debris shields for return to Earth.

Space walkers Rick Mastracchio and Clayton Anderson called out directions as a robot arm lifted the refrigerator-sized storage tank into place. One of the robotic snares got caught on the handling pin for the tank, but quickly was freed.

Then Mastracchio and Anderson had trouble bolting down the new tank on the sprawling framework that serves as the backbone of the space station. They tried using a pry bar on the mechanisms, but that didn't work and Anderson retreated to the air lock to get more tools.

The astronauts advised Mission Control to start coming up with a long-term solution in case the bolts would not cooperate.

The slot for the tank was emptied earlier in the spacewalk, when Mastracchio and Anderson popped out a nearly empty ammonia tank that had been on the space station for eight years. The ammonia is circulated through radiators to cool space station electronics.

Removing the old tank also had its share of difficulty.

One side of the boxy container got hung up on a mechanism, and Anderson had to tug it loose.

"I'm really getting good at this," Anderson said as the tank popped out. He had to use a pry bar during Friday's spacewalk to get the new replacement tank out of space shuttle Discovery.

As the space walkers were moving the old tank toward the robot arm for capture, Anderson got caught on a pit pin and lanyard. "Jiminy Christmas," he grumbled, freeing himself.

"Just go slow. It's fine. There's no rush," astronaut Dorothy Metcalf-Lindenburger assured him from inside.

With the space walkers serving as lookouts, the robot arm placed the old tank on a space station rail cart for temporary storage. "Keep it coming ... beautiful," Anderson said. The men strapped the tank down with several tethers.

During the third and final spacewalk of the mission Tuesday, the tank will be placed into the shuttle for return to Earth. NASA plans to refill the ammonia tank and fly it back to the space station this summer as a spare. That will be the next-to-last shuttle flight.